Merge branch 'en/pull-conflicting-options' into maint

"git pull" had various corner cases that were not well thought out
around its --rebase backend, e.g. "git pull --ff-only" did not stop
but went ahead and rebased when the history on other side is not a
descendant of our history.  The series tries to fix them up.

* en/pull-conflicting-options:
  pull: fix handling of multiple heads
  pull: update docs & code for option compatibility with rebasing
  pull: abort by default when fast-forwarding is not possible
  pull: make --rebase and --no-rebase override pull.ff=only
  pull: since --ff-only overrides, handle it first
  pull: abort if --ff-only is given and fast-forwarding is impossible
  t7601: add tests of interactions with multiple merge heads and config
  t7601: test interaction of merge/rebase/fast-forward flags and options

1 files changed, 224 insertions, 20 deletions

diff --git a/t/t7601-merge-pull-config.sh b/t/t7601-merge-pull-config.sh
index 52e8ccc933..1f652f433e 100755
--- a/t/t7601-merge-pull-config.sh
+++ b/t/t7601-merge-pull-config.sh
@@ -27,120 +27,324 @@ test_expect_success 'setup' '
 	git tag c3
 '
 
-test_expect_success 'pull.rebase not set' '
+test_expect_success 'pull.rebase not set, ff possible' '
 	git reset --hard c0 &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=true' '
 	git reset --hard c0 &&
 	test_config pull.ff true &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=false' '
 	git reset --hard c0 &&
 	test_config pull.ff false &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=only' '
 	git reset --hard c0 &&
 	test_config pull.ff only &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --rebase given' '
 	git reset --hard c0 &&
 	git pull --rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-rebase given' '
 	git reset --hard c0 &&
 	git pull --no-rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff given' '
 	git reset --hard c0 &&
 	git pull --ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-ff given' '
 	git reset --hard c0 &&
 	git pull --no-ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff-only given' '
 	git reset --hard c0 &&
 	git pull --ff-only . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set (not-fast-forward)' '
 	git reset --hard c2 &&
-	git -c color.advice=always pull . c1 2>err &&
+	test_must_fail git -c color.advice=always pull . c1 2>err &&
 	test_decode_color <err >decoded &&
 	test_i18ngrep "<YELLOW>hint: " decoded &&
-	test_i18ngrep "Pulling without specifying how to reconcile" decoded
+	test_i18ngrep "You have divergent branches" decoded
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=true (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_config pull.ff true &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=false (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_config pull.ff false &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=only (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_config pull.ff only &&
 	test_must_fail git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --rebase given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-rebase given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --no-rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-ff given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --no-ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff-only given (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_must_fail git pull --ff-only . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
+'
+
+test_does_rebase () {
+	git reset --hard c2 &&
+	git "$@" . c1 &&
+	# Check that we actually did a rebase
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 3 0 >expect &&
+	test_cmp expect actual &&
+	rm actual expect
+}
+
+# Prefers merge over fast-forward
+test_does_merge_when_ff_possible () {
+	git reset --hard c0 &&
+	git "$@" . c1 &&
+	# Check that we actually did a merge
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 3 1 >expect &&
+	test_cmp expect actual &&
+	rm actual expect
+}
+
+# Prefers fast-forward over merge or rebase
+test_does_fast_forward () {
+	git reset --hard c0 &&
+	git "$@" . c1 &&
+
+	# Check that we did not get any merges
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 2 0 >expect &&
+	test_cmp expect actual &&
+
+	# Check that we ended up at c1
+	git rev-parse HEAD >actual &&
+	git rev-parse c1^{commit} >expect &&
+	test_cmp actual expect &&
+
+	# Remove temporary files
+	rm actual expect
+}
+
+# Doesn't fail when fast-forward not possible; does a merge
+test_falls_back_to_full_merge () {
+	git reset --hard c2 &&
+	git "$@" . c1 &&
+	# Check that we actually did a merge
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 4 1 >expect &&
+	test_cmp expect actual &&
+	rm actual expect
+}
+
+# Attempts fast forward, which is impossible, and bails
+test_attempts_fast_forward () {
+	git reset --hard c2 &&
+	test_must_fail git "$@" . c1 2>err &&
+	test_i18ngrep "Not possible to fast-forward, aborting" err
+}
+
+#
+# Group 1: Interaction of --ff-only with --[no-]rebase
+# (And related interaction of pull.ff=only with pull.rebase)
+#
+test_expect_success '--ff-only overrides --rebase' '
+	test_attempts_fast_forward pull --rebase --ff-only
+'
+
+test_expect_success '--ff-only overrides --rebase even if first' '
+	test_attempts_fast_forward pull --ff-only --rebase
+'
+
+test_expect_success '--ff-only overrides --no-rebase' '
+	test_attempts_fast_forward pull --ff-only --no-rebase
+'
+
+test_expect_success 'pull.ff=only overrides pull.rebase=true' '
+	test_attempts_fast_forward -c pull.ff=only -c pull.rebase=true pull
+'
+
+test_expect_success 'pull.ff=only overrides pull.rebase=false' '
+	test_attempts_fast_forward -c pull.ff=only -c pull.rebase=false pull
+'
+
+# Group 2: --rebase=[!false] overrides --no-ff and --ff
+# (And related interaction of pull.rebase=!false and pull.ff=!only)
+test_expect_success '--rebase overrides --no-ff' '
+	test_does_rebase pull --rebase --no-ff
+'
+
+test_expect_success '--rebase overrides --ff' '
+	test_does_rebase pull --rebase --ff
+'
+
+test_expect_success '--rebase fast-forwards when possible' '
+	test_does_fast_forward pull --rebase --ff
+'
+
+test_expect_success 'pull.rebase=true overrides pull.ff=false' '
+	test_does_rebase -c pull.rebase=true -c pull.ff=false pull
+'
+
+test_expect_success 'pull.rebase=true overrides pull.ff=true' '
+	test_does_rebase -c pull.rebase=true -c pull.ff=true pull
+'
+
+# Group 3: command line flags take precedence over config
+test_expect_success '--ff-only takes precedence over pull.rebase=true' '
+	test_attempts_fast_forward -c pull.rebase=true pull --ff-only
+'
+
+test_expect_success '--ff-only takes precedence over pull.rebase=false' '
+	test_attempts_fast_forward -c pull.rebase=false pull --ff-only
+'
+
+test_expect_success '--no-rebase takes precedence over pull.ff=only' '
+	test_falls_back_to_full_merge -c pull.ff=only pull --no-rebase
+'
+
+test_expect_success '--rebase takes precedence over pull.ff=only' '
+	test_does_rebase -c pull.ff=only pull --rebase
+'
+
+test_expect_success '--rebase overrides pull.ff=true' '
+	test_does_rebase -c pull.ff=true pull --rebase
+'
+
+test_expect_success '--rebase overrides pull.ff=false' '
+	test_does_rebase -c pull.ff=false pull --rebase
+'
+
+test_expect_success '--rebase overrides pull.ff unset' '
+	test_does_rebase pull --rebase
+'
+
+# Group 4: --no-rebase heeds pull.ff=!only or explict --ff or --no-ff
+
+test_expect_success '--no-rebase works with --no-ff' '
+	test_does_merge_when_ff_possible pull --no-rebase --no-ff
+'
+
+test_expect_success '--no-rebase works with --ff' '
+	test_does_fast_forward pull --no-rebase --ff
+'
+
+test_expect_success '--no-rebase does ff if pull.ff unset' '
+	test_does_fast_forward pull --no-rebase
+'
+
+test_expect_success '--no-rebase heeds pull.ff=true' '
+	test_does_fast_forward -c pull.ff=true pull --no-rebase
+'
+
+test_expect_success '--no-rebase heeds pull.ff=false' '
+	test_does_merge_when_ff_possible -c pull.ff=false pull --no-rebase
+'
+
+# Group 5: pull.rebase=!false in combination with --no-ff or --ff
+test_expect_success 'pull.rebase=true and --no-ff' '
+	test_does_rebase -c pull.rebase=true pull --no-ff
+'
+
+test_expect_success 'pull.rebase=true and --ff' '
+	test_does_rebase -c pull.rebase=true pull --ff
+'
+
+test_expect_success 'pull.rebase=false and --no-ff' '
+	test_does_merge_when_ff_possible -c pull.rebase=false pull --no-ff
+'
+
+test_expect_success 'pull.rebase=false and --ff, ff possible' '
+	test_does_fast_forward -c pull.rebase=false pull --ff
+'
+
+test_expect_success 'pull.rebase=false and --ff, ff not possible' '
+	test_falls_back_to_full_merge -c pull.rebase=false pull --ff
+'
+
+# End of groupings for conflicting merge vs. rebase flags/options
+
+test_expect_success 'Multiple heads warns about inability to fast forward' '
+	git reset --hard c1 &&
+	test_must_fail git pull . c2 c3 2>err &&
+	test_i18ngrep "You have divergent branches" err
+'
+
+test_expect_success 'Multiple can never be fast forwarded' '
+	git reset --hard c0 &&
+	test_must_fail git -c pull.ff=only pull . c1 c2 c3 2>err &&
+	test_i18ngrep ! "You have divergent branches" err &&
+	# In addition to calling out "cannot fast-forward", we very much
+	# want the "multiple branches" piece to be called out to users.
+	test_i18ngrep "Cannot fast-forward to multiple branches" err
+'
+
+test_expect_success 'Cannot rebase with multiple heads' '
+	git reset --hard c0 &&
+	test_must_fail git -c pull.rebase=true pull . c1 c2 c3 2>err &&
+	test_i18ngrep ! "You have divergent branches" err &&
+	test_i18ngrep "Cannot rebase onto multiple branches." err
 '
 
 test_expect_success 'merge c1 with c2' '